In recent years, mobile wireless communications have become increasingly popular. Initial implementations of mobile wireless communications, for example in the form of cellular telephone networks, supported circuit switched voice communication services. The carriers developed short message service (SMS) technology to provide text and/or e-mail communications via the wireless networks. Today wireless carriers also offer packet data communication services to their mobile customers. The deployment of broadband packet-based wireless networks allows the carriers and other service providers to offer a variety of new services via Multimedia Messaging Service (MMS) technologies, which enable users of mobile devices to send and receive multimedia content, such as text, graphics, digital photographs, audio files and video clips, via non-real-time transmission.
The SMS service, for example, provides text messages for display on the mobile devices. In a typical implementation, SMS communications to/from a mobile device use a signaling channel over the airlink and use out-of-band signaling resources of the mobile phone network for transport to/from a server platform referred to as a SMSC (Short Message Service Center). The SMSC, for example, receives packet communications containing text messages and forwards the messages via the signaling resources and the signaling channels to the appropriate mobile devices. The SMSC will also receive similar messages from the mobile devices and forward them to servers or terminal devices accessible via an Internet Protocol (IP) packet data network. An MMS service operates in a similar manner using packet data communications capabilities of enhanced network architectures, for example, using a MMSC (Multimedia Messaging Service Center) to perform functions analogous to those of the SMSC.
The SMSC or MMSC type message service center is typically implemented on a server platform having appropriate network connectivity and programming. To provide the level of service reliability typically expected by the network operators' customers, the servers are implemented in a redundant manner. Thus, if a first server fails, then a second server should take over the duties of the first server. The second server may be referred to as secondary, or redundant, or sister, or backup, or matched, or mated to the first server.
One conventional approach provides locally redundant message servers, so that if a first (primary) message server fails, then a second (backup) message server can provide backup service. In this conventional approach, both message servers reside in a single geographic site. If either server fails, then the remaining server is able to handle its own traffic, plus the traffic from the failed server. The term “mated pair” may be the most accurate term for the conventional solution, because the second server is the backup for the first server, and simultaneously and symmetrically the first server is the backup for the second server.
FIG. 2 illustrates a conventional locally redundant approach for message servers in a SMSC. An SMSC is a collection of hardware that resides in an access MSC and uses the SS7 network and a group of store-and-forward messaging servers to send and receive text messages between mobile handsets and other communication entities. Geographic zone 210 is served by an access Mobile Switching Center (MSC-1) 220 and does not have a Short Message Service Center. A second geographic zone 230 is served by a second access Mobile Switching Center (MSC-2) 240, which includes a Short Message Service Center (SMSC-AB) 250 with locally redundant message servers. Short Message Service Center (SMSC-AB) may serve two or more geographic zones. In this example, the SMSC-AB may serve at least geographic zones 210 and 230 through their respective access MSCs 220 and 240. There are at least two types of MSCs: access and distribution. The distinction between access and distribution MSCs will be discussed in more detail elsewhere.
The SMSC-AB 250 has locally redundant message servers: Server A 254, and Server B 258. If one message server fails, then the remaining message server will handle the additional (“failover”) message server load. Short Message Service Center (SMSC-AB) may additionally have locally-redundant load balancers: Balancer-A 252, and Balancer-B 256. If one balancer fails, then the remaining balancer will handle the additional (“failover”) balancer load.
FIG. 3 illustrates internal detail for a conventional locally redundant Short Message Service Center (SMSC-AB) with locally redundant message servers (Server A 335, and Server B 345). Short Message Service Center (SMSC-AB) may also have locally redundant load balancers (Balancer-A 330, and Balancer-B 340). The message servers may communicate with mobile phones through an SS7 network, or communicate with distribution mobile service centers (MSC) through a router.
Note the redundant communication paths 351-358, 361, and 362. For example, if Balancer-A 330 fails, and Server B 345 fails, then Server A 335 is still functional. Specifically, Server A 335 may still communicate via path 354 to Balancer-B; and Balancer-B may communicate via path 352 to Ethernet switch 320; and Ethernet switch 320 may communicate with a router via path 351. Thus, this example has locally redundant message servers, and also has locally redundant balancers.
In its conventional configuration, all traffic that flows either from an ESME (SMPP Gateway, VM complex, etc.) to a mobile handset or vice versa passes through the locally redundant message server solution depicted in FIG. 3. IP traffic destined for a mobile handset is routed towards a VIP address which is originated from the MSC that houses the hardware which is provisioned to handle a particular customer base. For example, Server A 335 may be provisioned to handle traffic from customers in geographic zone 210, and Server B 345 may be provisioned to handle traffic from customers in geographic zone 230. Traffic from these two geographic zones may be routed to SMSC-AB 250. SMSC-AB is associated with a first VIP address for Server A (VIP-A), and with a second VIP address for Server B (VIP-B).
To summarize, this locally redundant solution illustrated by FIG. 3 advertises two VIP addresses from a single SMSC site, and the customer base is divided among the two VIP addresses.
The problem with locally redundant message servers is that a local catastrophe such as a hurricane may destroy a geographic site containing both the primary and the backup servers. Analysis shows that 99.999% availability may not be feasible using locally redundant message servers.
As discussed above, the hardware that is housed in SMSC-AB 250 is locally redundant so in the event of a single message server failure (or single balancer failure), then there are backup devices to handle the transactions of the failed hardware. Unfortunately, this local redundancy does not protect against a catastrophic failure (such as a hurricane) at the local site which may destroy or isolate all hardware at the local site.
Hence, as a result of this vulnerability to catastrophic failure at a local site, a need exists to increase survivability by physically separating the message servers, and locating the message servers at two different sites. This geographic separation will insure survival and availability of one of the message servers in case of a catastrophic failure at a local site. This geographic separation may be necessary in order to achieve 99.999% availability of at least one message server.